This invention relates to a transformer for use in an AC-DC converter or the like.
In general, a transformer is formed of a bobbin having a primary winding frame and a secondary winding frame, a primary coil wound around the primary winding frame, and a secondary coil wound around the secondary winding frame. A pair of connection pins are provided on the bobbin, and two ends of primary coil are respectively connected electrically to the corresponding connection pins. In this transformer, a pair of connection pins are connected to a domestic power supply line (of AC 100 V, for example), and the input voltage is reduced by the primary and secondary coils to obtain a predetermined necessary voltage through output terminals of the secondary coil (which is converted into a direct current if necessary).
To manufacture such a transformer, the primary and secondary coils are respectively wound around the primary and secondary winding frames by an automatic winding machine. However, if an automatic winding machine is used, the primary and secondary coils are wound in a tensed state, and there is a risk of disconnection of the primary and secondary coils by extension or contraction thereof caused by a change in atmospheric temperature or the like. The amount of heat developed in the primary coil is particularly large because a comparatively high voltage is applied to the primary coil, and the risk of disconnection of the primary coil is considerably high.
The pair of connection pins of such a transformer is electrically connected to a plug receptacle of domestic electric power supply. However, there is the problem of deterioration of the insulating performance of the transformer coils, in particular that of the primary coil, or occurrence of short-circuit between the primary and secondary coils when a very high voltage caused by, for example, lightning is applied to the domestic power supply line.